The invention relates to a method for grinding a workpiece and an apparatus for carrying out that method.
The components needed in engine and gear construction in particular require very exacting production tolerances. These exacting production tolerances are mainly achieved by fine working and subsequent precision working. Bearing seats or other portions of components subjected to great loading in later use are therefore often initially ground and subsequently further subjected to precision working, in order to achieve the required shape and surface quality with regard to service life and running properties.
The fine working and precision working are generally two successive operations on two machine tools respectively designed for each specific purpose. A disadvantage of this is that, on the one hand, the number of different machine tools greatly increases the investment expenditure required to realize the production of a specific component and that, on the other hand, the production costs for the component concerned are likewise increased by higher processing times with intermediate transporting operations. A further disadvantage is that the re-chucking in the machine tool performing the precision working can cause errors which prove to be disadvantageous for the production tolerances required.
Methods of precision working include honing in particular. Honing is a method of machining with bonded abrasive grain for improving or changing the shape, dimensional accuracy and surface quality of the workpiece, with the tool constantly engaging the surface of the workpiece. Honing is generally used after preceding fine working, such as grinding for example, as a finishing operation. So-called superfinishing in particular is also referred to as fine honing.
There are known machine tools for grinding and known machine tools for superfinishing for example (see company brochure IMPCO Machine Tools, USA, 1994). In addition to the disadvantages described above with regard to investment expenditure and production expenditure, the concept of two respectively different machine tools, for fine working and precision working, also represents a considerable development expenditure.
The invention is therefore based on the object of providing a method and an apparatus for working workpieces by means of which the geometry of the workpiece is worked in such a way as to maintain its dimensions and shape and provide it with the required surface quality, and the production time and consequently the unit costs of the workpiece are reduced considerably.
This object is achieved by a method having the features described herein and by an apparatus for carrying out the method having the features described herein.
In the method for grinding a workpiece, in particular a shaft part of a gear mechanism, the workpiece is clamped in place for working and the geometry of the workpiece is ground in such a way as to maintain its dimensions and shape. According to the invention, at least part of the surface of the workpiece is precision-worked at least partly at the same time as the grinding. The precision working is preferably performed by finishing.
According to one exemplary embodiment, the grinding and the precision working are performed on cylindrical and/or conical portions of the surface of the workpiece.
The apparatus used for carrying out the method according to the invention for grinding a workpiece is used in particular for grinding shaft parts, for example of a gear mechanism. The apparatus has a work-spindle headstock and a tailstock for clamping the workpiece in place as well as a grinding unit. The grinding unit is provided with at least one grinding spindle, which bears a grinding wheel for grinding the workpiece. The work-spindle headstock and the tailstock and/or the grinding unit are arranged movably in a controlled manner between the grinding unit and the workpiece for achieving relative movement in grinding, producing the desired workpiece geometry. According to the invention, the apparatus is provided with a precision-working unit, which can be moved according to the geometry of the workpiece, at least part of the surface of the workpiece being able to undergo precision working by means of the precision-working unit.
According to a preferred exemplary embodiment, the grinding unit and the precision-working unit are movable in such a way that at least some of the time they are simultaneously in engagement with the workpiece.
This makes it possible for the first time to carry out complete working of a workpiece, i.e. fine working and precision working, on one machine tool. This dispenses with external linkages for a number of operations, possibly with transporting procedures in between. Since it is no longer necessary for two different machine tools to be installed, for the fine working and the precision working, consequently the investment requirement, the overall costs and also the unit costs can be reduced considerably. In addition, the necessary space requirement is less, since there is a smaller number of machines with the same output on a defined production area. Furthermore, the processing and storage times are reduced as a result. Production can be made more transparent overall. Further advantages of the invention are that the number of machine suppliers can be reduced, since there is an identical machine concept for a machine which performs both the fine working and the precision working. This leads to considerable advantages in the servicing and maintenance area as well.
According to a further exemplary embodiment of the invention, the grinding unit and the precision-working unit are preferably arranged essentially opposite each other with respect to the longitudinal axis of the workpiece, so that the workpiece is clamped in place between the two working units. This has the advantage that both the grinding unit and the precision-working unit have freedom of movement, without hindering each other. In addition, with such an arrangement of the grinding unit and precision-working unit, simultaneous grinding and precision working of the workpiece are performed essentially over the entire length of the workpiece.
According to a further exemplary embodiment, it is also possible preferably to arrange the grinding unit and the precision-working unit essentially on one side of the workpiece with respect to the longitudinal axis of the workpiece. This is advantageous for example whenever only part of the surface of the workpiece has to be precision-worked and the length of the workpiece to be worked is great enough for the precision-working unit and the grinding unit not to hinder each other during simultaneous engagement with the workpiece
In one embodiment, the grinding unit has a carrier, to which two grinding spindles each with at least one grinding wheel are attached in such a way that they can swivel and are on a common infeed axis such that the grinding wheels can successively be brought into engagement with the workpiece. Such a grinding unit is advisable in particular whenever different surface contours of the workpiece are to be worked in such a way as to maintain its dimensions and shape by means of the grinding unit.
The precision-working unit is preferably designed as a precision-grinding unit or as a finishing unit. Both the precision-grinding unit and the finishing unit serve the purpose of achieving surface qualities of the workpiece or of part of the surface of this workpiece that lie in the range of the methods of production usually referred to as precision working.